The present invention relates to devices for intervening in the actuation of a vehicle throttle actuated by a driver controlled accelerator pedal typically connected to the throttle by a pivoted linkage including a tension cable. Under certain circumstances, as for example, sudden loss of wheel traction, it has been desired to provide an automatic way or means of intervening in the throttle actuation to prevent the driver from maintaining or increasing the throttle opening and to provide such intervention at a speed or rate greater than that of the physical reaction of the driver to the sudden loss of traction. In particular, it has been desired to provide throttle cable intervention in connection with the operation of vehicles equipped with anti-lock braking systems (ABS) which prevent wheel lockup upon application of the service brakes for stopping the vehicle. Vehicles equipped with ABS systems Provide imProved safety of operation by minimizing the risks of skidding and, therefore, enable the vehicle to stop in the minimum distance in the event of an emergency situation. ABS systems are, thus, a desirable feature and give the driver a sense of improved control of the vehicle. Where the driver is aware that the vehicle is equipped with ABS, it has also been found desirable to provide a traction control system which prevents wheel slippage in the power-on mode under conditions of vehicle operation on slippery road surfaces such as encountered in driving on ice or snow.
In order to provide traction control capable of responding to sudden loss of wheel traction at a rate faster than driver can physically react, it has been necessary to Provide electrical actuators for the engine throttle which can respond to a control signal generated by wheel slip sensors. However, there has been some reluctance in providing an all electric throttle actuation system for normal vehicle operation; and, it has been desired to retain the usual mechanical throttle tension cable linkage between the vehicle accelerator and the engine throttle. Therefore, it has been desired to provide an electrically operated throttle cable intervention device which can override the throttle actuation by the driver in the event of sudden loss of wheel traction but otherwise operates in the conventional mechanical cable tension mode from the vehicle accelerator. The problem has thus been to find a simple reliable and inexpensive servoactuator for throttle cable intervention to provide for changing the length of the throttle tension cable automatically by electrical operation of the servoactuator at a rate faster than the driver's physical reaction and to otherwise maintain normal mechanical throttle operation by the vehicle accelerator pedal when there is no loss of wheel traction.